A new analytical technique for the precise determination of ²³⁴U/²³⁸U isotope ratios was developed for low uranium concentration natural samples by MC-ICPMS to detect their natural isotopic variation. A reproducibility in ²³⁴U/²³⁸U ratio measurements of about 0.18% was obtained from approximately 1.6 ng uranium through the correction of the mass discrimination effect with a reference ²³⁵U/²³⁸U ratio without ²³³U–²³⁶U double spike method. The precision and sample amounts required were improved by more than one order of magnitude compared to those achieved by the conventional alpha spectrometry, and the analysis time of less than 10 minutes per sample was shorter than that of TIMS. The validity of our method was confirmed from a coral reference material JCp-1, with 1.1414±0.0025 and 1.1426±0.0025 as the ²³⁴U/²³⁸U activity ratio, which was consistent with previously reported values. This technique was applied to water samples, and a natural ²³⁴U/²³⁸U isotopic variation was observed in two spring water samples with different redox conditions and groundwater ages. The data obtained in this study demonstrated that this technique will be useful for the hydrological study using ²³⁴U/²³⁸U ratios for samples with small uranium contents including groundwater research.

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is a powerful analytical technique which enables highly specific determination of drugs even at the ng/L level, especially for hair samples from victims of drug-facilitated sexual assault. However, there are issues that coexist with such level of sensitivity. We experienced a false-positive result wherein a diphenhydramine (DPH, an OTC sleep aid) peak constantly appeared at trace levels even in the blank tests. In this study, the cause of this phenomenon was investigated to ensure the reliability of analysis. As a results, it has been revealed that the ultrapure water, prepared from tap water for making the mobile phases, contained DPH as an impurity at pg/L level. DPH in the mobile phase was probably concentrated at the top of the reverse-phase LC column by the gradient program, and then was eluted with increased percentage of organic solvent in the mobile phase. DPH in the ultrapure water is probably attributed to contamination of aquatic environment by pharmaceuticals and personal care products (PPCPs).Thus, in the high-sensitivity analysis of drugs, great attention should be paid to the fact that ultrapure water, used for sample preparation or mobile phases, can contain very small amounts of PPCPs.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), which provides high sensitivity and high resolution, has been used for the analysis of biopolymers. In the past decade, MALDI-TOF MS has been utilized in clinical fields around the world to identify microbial species. However, serotype or strain discrimination of the same bacterial species is difficult by MALDI-TOF MS. Different methods such as PCR and immunoassay are performed for the serotype identification. However, these assays required previous preparation and selection of each probe for every candidate, which is extremely complicated. This study developed a method to measure different O antigens from a single colony of E. coli by MALDI-TOF MS within one hour. From mixtures of E. coli strains with different O antigens, each colony can be assigned without column or HILIC manipulation. This O antigen (serotype) identification method, combined with the conventional MALDI biotyping (species) method toward ribosomal protein, would be a powerful technique for microorganism identification.

A ¹³C-tracer analysis using mass spectrometry was developed for investigating dynamics of lipid metabolism in budding yeast Saccharomyces cerevisiae, a model eukaryote organism. The ¹³C-tracer experiment using [U-¹³C] glucose combined with the non-target lipidomic using LC-QTOF/MS revealed different labeling dynamics ¹³C-labeling of among class of phospholipids.

Epimetabolite is defined as analogues of known metabolites with different substructures. The rapid development of high-resolution mass spectrometry (HRMS) and some data mining tools has contributed to detecting and identifying a few epimetabolites that could play an important role as biological functions. However, almost all epimetabolites have not been identified because a generally applicable method for the comprehensive annotation of epimetabolites had not been developed. In the present study, we have proposed an advanced methodology for comprehensive structural elucidation of unidentified hydrophilic metabolites by a combination of stable isotope labeling, unified-HILIC/AEX/HRMS/MS analysis, data mining techniques, and metabolite annotation using in silico epimetabolite database (IEMDB). In fact, we successfully annotated 444 novel epimetabolite candidates in E. coli. Our method has several advantages over conventional techniques and represents a potentially useful tool for structural elucidation of comprehensive epimetabolites.

Space travel induces stresses that provoke health problems, and concomitantly induces the expression of Nrf2 (NF-E2-related factor-2) target genes that mediate adaptive responses to oxidative and other stresses. While the variation of lipid species in white adipocytes (eWAT) have been identified, detailed changes of lipid profiles, such as the level of fatty acid, remain unknown. Therefore, we have analyzed eWAT and liver tissues of flight mice and ground control including wild type and Nrf2 knockout mice by means of the lipidomic profiling using a UHPLC-FTMS. The level of eicosapentaenoic acid (EPA) type of phospholipids were significantly increased after space flight, suggesting that EPA may be the key factor for the novel function involved in antioxidant effects of Nrf2 in the space flight.

In risk management and monitoring of chemical substances, it is important to comprehensively identify by-products and impurities that are unintentionally released due to disasters and accidents. By measuring samples with a high-resolution mass spectrometer and obtaining comprehensive accurate mass spectra over a wide mass range, it is expected to be possible to identify not only chemical substances assumed to be released in disasters and accidents but also other substances. This paper briefly introduces overseas reports and the efforts of the authors regarding the exhaustive analysis of chemical substances using a high-resolution mass spectrometer, using a fire accident as an example.